Noncapillary silk suture and method of preparing the same



Patented Mar. 12, 1940 v UNITED STATES NONCAPILLARYSILK SUTURE ANDMETHOD "OF PREPARING THE SAME Theodore F. Bradley, Stamford, Conn,assignor to American Cyanamid Company, New

York,

N. Y., a corporation of Maine I NoDrawing. Application June 16, 1938,Serial No. 214,147

9 Claims. (Cl. 128-3355) The present invention relates to a method ofmaking a noncapillary silk suture for surgical purposes and the sutureper se. 7

Silkthreads, made by twisting or braiding a number of degummed andcleaned raw silk filaments, have been used in surgery as suture materialfor many years. However, when such a silk suture is embedded in infectedtissue, bacteria are harbored in its interstices and the suture becomesa nidus of infection which does not subside until the silk sloughs outor is removed surgically. Because of its capillarity, there is alwaysthe possibility of the exposedend of a silk suture acting as a wick tocarry infection into the tissue. Thematerial, therefore, has never comeinto general surgical use for this purpose.

It is a principal object of the invention to produce a silk suture madeof a number of silk threads, twisted, braided, woven or otherwiseassociated together into a strand, which will be substantiallynoncap-illary, and this object can most effectively be accomplished bycoating such suture material with a composition which will present anunbroken surface to moisture.

The proposal toreducethecapillarity of silk sutures is not a new one.Many attempts have been made to this end and while it has been found notparticularly difficult to-treat a braided or twisted surgical silk so asto produce a satisfactory degree of noncapillarity, yet such treat--ment resulted in lending undesirable characteristics to the product orwas unsatisfactory for other reasons.

A surgical silk suitable for useas a suture must be soft, pliable,nonacidic, noncorrosive and physiologically harmless and be capable ofwithstanding heat or chemical sterilization. These factors havegenerally stood in the way of the production of a successfulnoncapillary surgeons silk, for any treatment which decreasedcapillarity was objectionable because such product did not meet theother necessary qualifications or because the stringent conditions ofsterilizawithout detrimental effect.

silk suture by applying to the silk suture stock, hereinafter referredto as a strand, a composition including ethyl cellulose in a volatilesolvent and then permitting or inducing the solvent to evaporate. Underthese conditions, the ethyl cellulose forms an unbroken film on theexterior periphery of the suture strand and even penetrates the same toa desired extent, whereby the capillarity of the strand is reduced.

A noncapillary suture thus produced will withstand the usual heat and/orchemical st'erilization without substantial decrease in itsnoncapillarity. Where the sterilization treatment consists in contactwith hot liquids, such as hot mineral 'oil, the suture will withstandthe necessary high temperatures for the required periods Such heatsterilization treatment in oil is even beneficial in that it hasatendency to maintain the pliability of the suture, and in use even whenthe excess oil is removed, a slight film thereof remains which, due toits water repellency, assists in maintaining the noncapillarity of theproduct.

The invention further contemplates a substantially noncapillary silksuture product in which the silk strand or strands are provided with oneor more coatings of ethyl cellulose with or without an additionalsuperficial coating of oil.

Alarge number of coatingand impregnating compositions were found to besatisfactory from the standpoint of actually reducing capillarity to thedesired degree when applied to twisted or braided silk suture stock butresulted in lending stillness, u'npliability or other undesirablecharacteristics to the product, or the noncapillarity was materiallydestroyed when such products were subjected to heat and/or chemicalsterilization or to other conditions to which sutures may be normallysubjected.

Ethyl cellulose was found to be of outstanding value in that it met allof the stringent requirements without producing detrimental eifectswhile at the same time producing reduction in capillarity to the desireddegree with optimum permanence.

In preparing the ethyl cellulose solution with which the silk stock isto be treated, ethyl cellulose of various viscosities and differentsolvents may be employed. While ethyl cellulose of viscosities of from10 to centipoises has been 50 used for these compositions, such as themethyl 5 or ethyl ether of ethylene glycol, toluene, ethanol or mixturesthereof, as well as other known solvents, the proportions being variedto give the desired concentration of ethyl cellulose. Mis cible diluentsmay also be employed and where these are noninflammable, such as carbontetra chloride, their use may be desirable under some circumstances.

The preferred coating composition comprises the following substances insubstantially the proportions specified:

Solution A Grams Ethyl cellulose20 centipoise grade 40 Toluene 120Ethanol 40 200 (20% solids) Solution B Grams Solution A 40 Ethanol 10Toluene 50 100 (8% solids) Suture stock silk may then be immersed in,sprayed or otherwise contacted with, such a solution for from one to twominutes, the excess solution removed and then the coated strand airdriedor preferably at some elevated temperature to remove all of the volatilesolvent. This operation may be repeated as many times as necessary inorder to produce a coating of the desired thickness or Weight, dependentupon the circumstances. In order to reduce fire hazard due to theinfiammability of the above solvents, requisite amounts of carbon tetrachloride may be added thereto as desired.

After the silk has thus been treated to render it noncapillary, it maybe out into the required lengths, wound into small coils, placed inglass tubes, which are filled with a light mineral oil and then sealedby fusion of the glass, the sealed tubes may then be placed in anautoclave and heat sterilized. When this is complete, the tubes areready for packaging. While the above method of sterilization ispreferred, other standardized procedures may likewise be employed.

While the invention has been described with specific reference tocertain embodiments, it is to be understood that it is not to be limitedthereto but is to be construed broadly and restricted solely by thescope of the claims.

"coated with ethyl cellulose and having a superficial exterior coatingof oil.

3. A substantially noncapillary non-water absorptive silk suturecomprising a silk strand coatedwith ethyl cellulose and having asuperficial exterior coating of mineral oil.

4. A method of making a substantially noncapillary silksuture whichincludes the following steps: contacting a silk strand with a solutionof ethyl cellulose in an organic solvent, removing the strand from thesolution and evaporating the solvent from the ethyl cellulose so as toproduce an adherent coating of the latter on the strand.

5. A method of'making a substantially noncapillary silk suture whichincludes the following steps: immersing a silk strand in a solution ofethyl cellulose in an organic solvent, removing the strand from thesolution, removing the excess solution from the strand and drying thestrand.

6. A method of making a substantially noncapillary silk suture whichincludes the following steps: immersing the silk strand in ethylcellulose dissolved in a mixture of toluene and ethyl alcohol,removingthe strand from the solution and drying the strand.

7. A method of making a substantially noncapillary silk suture whichincludes the following steps: immersing the silk strand in a solution of20 centipoise viscosity ethyl cellulose in an organic solvent, removingthe strand from the solution anddrying the strand.

8. A method of making a substantially noncapillary silk suture whichincludes the following steps: immersing a silk strand in an 8% solutionof 20 centipoise viscosity ethyl cellulose in an organic solvent,removing the strand from the solution and drying the strand.

9. A method of making a substantially noncapillary silk suture whichincludes the following steps: immersing a silk strand in a solution ofethyl cellulose in an organic solvent, removing the strand from thesolution and evaporating the solvent from the ethyl cellulose so as toproduce an adherent coating of the latter on the strand and sterilizingthe coated strand in mineral oil.

THEODORE F. BRADLEY.

